For compression of video data, a plurality of video standards has been developed. Such video standards are, for example, MPEG-2, MPEG-4 and H.264/MPEG-4 AVC. As a successor to H.264/MPEG-4 AVC, High Efficiency Video Coding (HEVC) is currently under joint development by the ISO/IEC Moving Picture Experts Group (MPEG) and ITU-T Video Coding Expert Group (VCEG).
According to HEVC, one picture is divided into largest coding units (LCUs), one or more coding units of each LCU are encoded by generating a prediction block using inter prediction or intra prediction. The difference between an original block and the prediction block is transformed to generate a transformed block, and the transformed block is quantized using a quantization parameter and one of a plurality of predetermined quantization matrices. The quantized coefficients of the quantized block are scanned by a predetermined scan type and then entropy-coded. The quantized coefficients are inversely quantized and inversely transformed to generate a residual block which is combined with the prediction block to generate reconstructed image. The reconstructed image is adaptively filtered using a deblocking filter to remove blocking artifacts.
FIG. 1 is a conceptual diagram illustrating a procedure of determining the boundary strength according to HEVC under development.
As shown in FIG. 1, boundary strength is determined on every edge of all 4×4 blocks in the first step, and then the final boundary strength is determined on edges of 8×8 blocks. The edge of the 8×8 block is comprised of two consecutive edges of 4×4 blocks. The boundary strength of the edge of the 8×8 block is determined as a maximum of boundary strength of two edges that constitute the edge of the 8×8 block. But, the technique of deblocking filter described in HEVC under development deteriorates encoding and decoding performance because the technique is too complicated.
Therefore, the standardization of HEVC under development focuses on the technique reducing the complexity of the deblocking filter as well as improving the performance of the deblocking filter. In particular, new techniques able to reduce operational complexity and memory capacity required to perform the deblocking filtering are required because HEVC focuses on encoding and decoding ultra high-definition image.